1. Field of the Invention
The present invention relates to an airbag device which protects a vehicle passenger from shock when a vehicle collision has occurred.
2. Related Art
An airbag device that uses an inflatable airbag to soften shock applied to a vehicular passenger in the event of a vehicle collision is well-known. In such an airbag device, an electronic control unit is used to deploy the airbag. The electronic control unit determines the occurrence of a vehicle collision based on a signal output from a deceleration sensor which is installed inside or outside of the electronic control unit and which detects deceleration when the vehicle collision has occurred. More specifically, the electronic control unit determines the occurrence of the vehicle collision by comparing the detected deceleration with a predetermined value. The predetermined value is preset and stored in the electronic control unit in accordance with the type of vehicle on which the airbag device is mounted or the attachment position of the sensor and electronic control unit.
Because the electronic control unit stores the different predetermined values, an unsuitable electronic control unit may be installed in a particular vehicle. Because the same housings or casings are used for various types of the airbag devices to reduce their cost, external appearances of the electronic control units are usually substantially similar adding to the possibility of installing an unsuitable device in a vehicle. To avoid such problem, a conventional electronic control unit includes, for example, an identification on its housing. Operators select a suitable electronic control unit based on this indentification, and they install the selected electronic control unit in the vehicle. However, there is no guarantee that the operators will not make a mistake with regard to selection of the appropriate electronic control unit.
If an unsuitable electronic control unit is selected and installed in the vehicle, the airbag device can not inflate its airbag at the proper time because the predetermined value stored in the electronic control unit for determining the vehicle collision does not match the vehicle in which the electronic control unit is installed.
To avoid such an undesirable situation, conventionally, the following measures are adopted. The electronic control unit outputs an identification signal from its output terminal, and the identification signal is input to an identification apparatus connected to the output terminal. The identification apparatus determines, based on the identification signal, whether the electronic control unit is correct or not, and shows the result.
However, in the conventional airbag device, there is a problem in that the flexibility concerning the configuration of the electronic control unit and a mounting position of the electronic control unit on the vehicle is limited. That is, because the identification apparatus must be connected to the output terminal of the electronic control unit for identifying the type of the electronic control unit, the control unit must be mounted on the vehicle so that the identification apparatus can be easily connected to the output terminal.
Furthermore, if the output terminal is not provided in the electronic control unit, it is difficult to determine whether an electronic control unit, which is suitable for the vehicle, is installed after the airbag device has mounted on the vehicle. For example, in an airbag device where the electronic control unit is installed in a steering unit along with an airbag and inflator for inflating the airbag, the electronic control unit usually does not provide the output terminal.